The present invention relates generally to brake pedals, and more specifically, to a brake pedal assembly with a variable ratio linkage.
Vehicles, and in particular automotive vehicles, include a brake system for controlling the movement of the vehicle. Conventional brake systems include a brake pedal for transmitting a braking force from the vehicle operator to the wheels of the vehicle. The brake pedal is operatively coupled to a brake booster via a push rod. The brake booster is operatively connected to a master cylinder, and the master cylinder is operatively connected to a braking mechanism via brake lines. The braking mechanism is coupled to a wheel of the vehicle and applies the force to the wheel to slow down the rotational movement of the wheel.
Various factors influence the overall efficiency of the brake system. Examples of some of these factors include the size of the brake booster, the master cylinder diameter and radius of the tires, the brake pad material and the pedal lever ratio. At the same time, the brake system must comply with regulatory requirements regarding braking distance and the amount of force required to slow down the vehicle.
Pedal lever ratio refers to the geometric relationship between the levers that make up the brake pedal assembly. A typical brake pedal assembly includes a pedal arm, and an upper end of the pedal arm is pivotally mounted to a support bracket. The support bracket is fixedly mounted to the vehicle. A pedal pad is mounted to a lower end of the pedal arm for depression by the driver's foot. The brake booster push rod is attached to the pedal arm at a location between the pedal pad and the pivot point at the upper end of the pedal arm. The feel and effectiveness of the braking action experienced by the operator can be varied by changing the “pedal ratio”. The “pedal ratio” is expressible as a ratio a/b, where “a” is the distance between the pivot point for the pedal arm and the actuation point on the pedal pad, and “b” is the distance between the pivot point and the booster rod attachment point. In general, the lower the value of the pedal ratio, the greater the distance the brake rod pivot point and booster push rod travel, relative to the distance traveled by the pedal pad. A high pedal ratio can be effective, but the long pedal travel results in a “spongy” feel to the brakes. Conversely, a low pedal ratio is the result of a shorter pedal travel, however, the shorter pedal travel results in an abrupt or sharp braking action.
Various types of variable ratio brake pedals are known in the art. For example, U.S. Pat. No. 4,615,235 to Horvath dated Oct. 7, 1986 discloses a variable ratio brake pedal system. This system includes a first lever pivotally mounted on an arcuately movable pedal arm. One end of the first lever is attached to the brake booster push rod. The other end of the first lever is pivotally attached to a pivot control lever. The pivot control lever is fixedly attached at the other end. An upper end of the pedal arm is fixedly attached to a portion of the vehicle. Thus, actuation of the brake pedal increases the pedal ratio relative to the travel of the brake pedal, by a factor of about two. While this system works, the large angular displacement at the second pivot point, between the brake booster rod and the first lever, may result in excessive stress on the brake booster rod.
Another example of a variable brake pedal assembly is disclosed in U.S. Pat. No. 6,070,488 to Yabusaki et al., dated Jun. 6, 2000. This system includes a suspended pedal attached to a pedal bracket having a main bracket and a sub-bracket. A V-shaped swing link connects the brake pedal and a push rod. If a predetermined external force is applied to the front of the vehicle, an extending portion of the sub-bracket is pressed by the main bracket and swings rearward of the vehicle and a clevis at the end of the push rod is forced in toward the front side of the vehicle by a front surface of the extending portion of the sub-bracket. The brake pedal swings around the mounting bolt toward the front side of the vehicle via the swing link, and the link and the pedal pad is displaced towards the front side of the vehicle. The movement of the pedal pad towards the front side of the vehicle protects the driver's legs from contacting a portion of the vehicle, such as the steering column. While this system works in counteracting the effect of an external force applied to the front of the vehicle with respect to the pedal, it does not vary the pedal ratio under typical driving conditions.
In larger vehicles, such as SUVs, more force is required to control the movement of the vehicle, and a higher pedal ratio may be required, especially at the beginning of the braking action. The displacement of the brake pedal from an initial, resting position to a fully depressed portion is referred to as pedal stroke. Thus, there is a need in the art for a brake pedal assembly in which the relative position of the brake rod attachment point changes with respect to the pivot position of the pedal arm, to provide a pedal ratio multiplier or variable pedal ratio that increases during the stroke of the brake pedal.